I have determined the nucleotide sequence of the tetracycline resistance region of plasmid pBR322. The sequence of the tet genetic region appears to encode at least two proteins. I have snythesized three peptides which correspond to protions of the amino acid sequences of the two predicted proteins, coupled these to an immunogenic carrier protein and innoculated rabbits with coupled peptides. It is the aim of the proposed research to use the antipeptide sera to identify the tet proteins within plasmid bearing bacteria and then to purify the proteins using the antisera as an assay. The proteins will be localized within cells by cell fractionation and immunoassay. The purified proteins will be tested for various functional properties such as tetracycline binding, metal ion binding and ability to protect an in vitro protein synthesis system from tetracycline inhibition. The gene for the tet repressor on pSC101 will be sequenced and the repressor protein will be purified by making antibodies againstsynthetic peptides corresponding to the protein predicted by the DNA sequence. The mechanism of repression of tet resistance by repressor will be analyzed. These studies should provide greater insight into the molecular basis of tet resistance. The assays developed for the purified proteins should allow simple pharmaceutical tests for tetracycline derivatives and analogues. the ideal tetracycline-like antibiotic would not induce the resistance mechanism and would be imprevious to it if it were induced.